DE102007013964A1 - Process for removing and recycling condensable components from chlorine-containing gas streams - Google Patents

Abstract

It is a three-stage process for the recovery of chlorine from a chlorine-containing exhaust stream, in which the exhaust gas stream is compressed in a first stage A), cooled in a second stage B) coming from the first stage exhaust stream and the chlorine contained therein partially or completely Condensation is separated together with a part of the remaining condensable or soluble components contained in the exhaust gas and the resulting condensate is placed in a built-in condensation zone below the gas contact zone with the incoming in the second stage exhaust stream in countercurrent in contact and in a third stage C) condensate coming from the second stage is worked up in a rectification column into a chlorine-rich bottom stream and a gaseous and a liquid, low-chlorine top stream extraction of chlorine.

Description

The The invention is based on a method for the production of chlorine a chlorine-containing exhaust gas stream, in particular the chlorine-containing exhaust gas stream a chemical production process.

In the vast majority of chemical processes are waste gas streams consisting of multicomponent mixtures. The components of the exhaust gas streams can be over- or subcritical. Of others may be considered inert in the sense of legislation Components or as pollutants.

• a) eine möglichst vollständige Abscheidung der im Abgas enthaltenen Schadstoffe sowie
• b) die wirtschaftlich zweckmäßige Rückführung der betreffenden Schadstoffe in den Produktionsprozess, so es sich gleichzeitig um Wertstoffe handelt.

In any case, the process-technical goal is the treatment of corresponding currents

• a) as complete as possible separation of the pollutants contained in the exhaust gas and
• b) the economically expedient return of the relevant pollutants into the production process, which are also recyclables.

Especially in the chloralkali electrolysis, the HCl electrolysis, the Deaconprozess as well as in other chlorochemical processes exhaust flows consisting of chlorine, carbon dioxide, nitrogen or oxygen as well other secondary components.

Due to the high proportion of components that can not be condensed under atmospheric conditions, such as oxygen, nitrogen and CO ₂ , the chlorine contained in these exhaust gas streams is generally not recovered, but is removed from the exhaust gas by means of chemical absorption processes and decomposed (see, for example, US Pat. EP 0406675 B1 . US3984523 . DE 2413358 ).

task The invention is to develop a process that the workup chlorine-containing waste gas streams simplified and absorption process avoids as described above.

The however, the present invention enables recovery the chlorine contained in the exhaust, creating a downstream chemical absorption of the chlorine can be omitted or the operating costs of such Absorption can be significantly reduced.

• – in einer ersten Stufe der Abgasstrom auf einen Druck von höchstens 15 bar (15000 hPa) gebracht wird;
• – in einer zweiten Stufe der aus der ersten Stufe kommende Abgasstrom gekühlt und das darin enthaltene Chlor teilweise oder vollständig durch Kondensation zusammen mit einem Teil der übrigen im Abgas enthaltenen kondensierbaren oder löslichen Komponenten abgetrennt wird und das hierbei anfallende Kondensat in einer unterhalb der Kondensationszone eingebauten Gas-Flüssigkeitskontaktzone mit dem in der zweiten Stufe eintretenden Abgasstrom im Gegenstrom in Kontakt gebracht wird;
• – in einer dritten Stufe das aus der zweiten Stufe kommende Kondensat in einer Rektifikationskolonne in einen chlorreichen Sumpfstrom sowie einen gasförmigen und einen flüssigen, chlorarmen Kopfstrom aufgeteilt wird und der chlorreiche Sumpfstrom zur Gewinnung von Chlor aufgearbeitet wird.

The invention relates to a process for the extraction of chlorine from an exhaust gas stream, in particular the exhaust gas stream of a chemical production process, characterized in that

• - In a first stage, the exhaust gas flow is brought to a pressure of at most 15 bar (15000 hPa);
• Cooled in a second stage of the exhaust gas stream coming from the first stage and the chlorine contained therein is partially or completely separated by condensation together with a part of the other condensable or soluble components contained in the exhaust gas and the resulting condensate in a built-in below the condensation zone gas Liquid contact zone is brought into contact with the incoming in the second stage exhaust stream in countercurrent;
• - In a third stage, the condensate coming from the second stage is divided in a rectification column into a chlorine-rich bottom stream and a gaseous and a liquid, low-chlorine top stream and the chlorine-rich bottom stream is worked up to recover chlorine.

In In a preferred method, the exhaust stream contains at least Nitrogen, oxygen, carbon dioxide and chlorine.

In a preferred embodiment of the new method in the first stage the exhaust gas flow to a pressure of 20 to 60 bar, preferably 30 to 40 bar, set.

In Another preferred embodiment of the new method is the condensation temperature in the second and the third stage -20 ° C to -80 ° C.

A particularly preferred variant of the new method is characterized in that that between the gas stream coming from the first stage and the heat exchanged condensate coming from the third stage and the condensate from the third stage is evaporated. Herewith an energetically favorable driving style of the method is made possible.

In Another particularly preferred embodiment of the new Procedure will still be between the exiting from the second stage Gas stream and the gas stream entering the second stage heat exchanged.

The Method can preferably also be carried out so that first, those leaving the second and third stages Gas streams are mixed to subsequently with heat entering the second stage gas stream To deceive.

The method is particularly preferably used when the chlorine-containing exhaust gas stream comes from a production process for the production of chlorine from hydrogen chloride and oxygen, in particular a catalyzed gas phase oxidation of hydrogen chloride or a non-thermal reaction of hydrogen chloride and oxygen.

Prefers As already described above, a chlorine-containing exhaust gas stream of used as the Deacon process known catalytic process. in this connection becomes hydrogen chloride with oxygen in an exothermic equilibrium reaction oxidized to chlorine, whereby water vapor is obtained. The reaction temperature is usually 150 to 500 ° C, the usual reaction pressure is 1 to 25 bar. Since it is an equilibrium reaction, it is expedient to work at the lowest possible temperatures at which the catalyst still has sufficient activity. Furthermore, it is expedient to oxygen in superstoichiometric Use quantities of hydrogen chloride. For example, it is usual a two- to fourfold oxygen excess. There no Selective loss can be feared It may be economically advantageous at relatively high pressure and accordingly longer at normal pressure Dwell time to work.

suitable contain preferred catalysts for the Deacon process Ruthenium oxide, ruthenium chloride or other ruthenium compounds Silica, alumina, titania or zirconia as Carrier. Suitable catalysts may be, for example by applying ruthenium chloride to the carrier and subsequent drying or drying and calcination are obtained. Suitable catalysts may be added to or in place of a ruthenium compound also compounds of other precious metals, for example, gold, palladium, platinum, osmium, iridium, silver, copper or rhenium. Suitable catalysts can also contain chromium (III) oxide.

The catalytic hydrogen chloride oxidation can be adiabatic or isothermal or approximately isothermal, discontinuous, but preferably continuously as flow or fixed bed process, preferred as a fixed bed process, particularly preferably in tube bundle reactors on heterogeneous catalysts at a reactor temperature of 180 to 500 ° C, preferably 200 to 400 ° C, more preferably 220 to 350 ° C and a pressure of 1 to 25 bar (1000 to 25000 hPa), preferably 1.2 to 20 bar, more preferably 1.5 to 17 bar and in particular 2.0 to 15 bar are performed.

usual Reaction apparatus in which the catalytic hydrogen chloride oxidation are carried out, are fixed bed or fluidized bed reactors. The catalytic hydrogen chloride oxidation may also be preferred be carried out in several stages.

at the isothermal or almost isothermal driving style also in adiabatic driving, several, ie 2 to 10, preferably 2 to 6, more preferably 2 to 5, in particular 2 to 3, series reactors with intercooling be used. The oxygen can either be complete together with the hydrogen chloride before the first reactor or over the different reactors are distributed. This series connection individual reactors can also be combined in one apparatus become.

A Another preferred embodiment of the one for Method suitable device is that one is a structured Catalyst bed begins, in which the catalyst activity increases in the flow direction. Such structuring the catalyst bed can by different impregnation the catalyst support with active material or by different Dilution of the catalyst with an inert material. As an inert material, for example, rings, cylinders or Balls of titanium dioxide, zirconium dioxide or mixtures thereof, alumina, Steatite, ceramic, glass, graphite or stainless steel can be used. In the preferred use of shaped catalyst bodies, the Inert material prefers similar outer Have dimensions.

When Catalyst moldings are suitable moldings with any shapes, preferably tablets, rings, cylinders, stars, Cartwheels or balls, particularly preferred are rings, Cylinder or star strands as a shape.

When Heterogeneous catalysts are particularly suitable ruthenium compounds or copper compounds on substrates, which also doped ruthenium catalysts are preferred. Suitable carrier materials are, for example, silicon dioxide, Graphite, titanium dioxide with rutile or anatase structure, zirconium dioxide, Alumina or mixtures thereof, preferably titanium dioxide, zirconium dioxide, Alumina or mixtures thereof, more preferably γ- or δ-alumina or mixtures thereof.

The copper or ruthenium-supported catalysts can be obtained, for example, by impregnation of the support material with aqueous solutions of CuCl ₂ or RuCl ₃ and optionally a promoter for doping, preferably in the form of their chlorides. The shaping of the catalyst can take place after or preferably before the impregnation of the support material.

For doping the catalysts are suitable as promoters alkali metals such as lithium, sodium, potassium, rubidium and cesium, preferably lithium, sodium and potassium, more preferably potassium, alkaline earth metals such as magnesium, calcium, strontium and barium, preferably magnesium and calcium be particularly preferably magnesium, rare earth metals such as scandium, yttrium, lanthanum, cerium, praseodymium and neodymium, preferably scandium, yttrium, lanthanum and cerium, more preferably lanthanum and cerium, or mixtures thereof.

The Shaped bodies can then be used in a Temperature of 100 to 400 ° C, preferably 100 to 300 ° C. for example, under a nitrogen, argon or air atmosphere dried and optionally calcined. To be favoured the moldings initially at 100 to 150 ° C. dried and then at 200 to 400 ° C. calcined.

Of the Hydrogen chloride conversion in single pass may be preferred to 15 to 90%, preferably 40 to 85%, more preferably 50 to 70% are limited. Unreacted hydrogen chloride can after Partial or complete separation into the catalytic Hydrogen chloride oxidation be recycled. The volume ratio from hydrogen chloride to oxygen at the reactor inlet preferably 1: 1 and 20: 1, preferably 2: 1 and 8: 1, more preferably 2: 1 and 5: 1.

The Reaction heat of catalytic hydrogen chloride oxidation can advantageously for the production of high pressure water vapor be used. This can be used to operate a phosgenation reactor and or of distillation columns, especially of isocyanate distillation columns be used.

In This is the last step of the Deacon process in the Deacon reaction formed chlorine separated. The separation step usually comprises several Stages, namely the separation and optionally recycling of unreacted hydrogen chloride from the product gas stream of catalytic hydrogen chloride oxidation, the drying of the obtained, essentially chlorine and oxygen-containing stream and the Separation of chlorine from the dried stream.

The Separation of unreacted hydrogen chloride and formed Water vapor can be obtained by condensing out aqueous hydrochloric acid from the product gas stream of hydrogen chloride oxidation by cooling respectively. Hydrogen chloride can also be in dilute hydrochloric acid or water are absorbed.

Of the the new process underlying chlorine-containing exhaust gas stream can z. B. the remaining after the separation of the chlorine residual gas or to be a part of it.

In the first stage of the preferred new process is the chlorine-containing Exhaust gas stream is compressed to the required process pressure. The height the pressure to be selected depends essentially of the required residual chlorine content of the exhaust gas at the outlet of the new Method and of the subsequent condensation / rectification steps available cold levels. That too dialing pressure level is preferably 10 to 60 bar (10,000 to 60,000 hPa) and more preferably 30 to 50 bar.

The Adjustment of the pressure level is in particular using the conventional pressure booster machines for Gas streams, z. B. piston compressors, turbo compressors or liquid ring pumps. Furthermore, can the compression preferably one or more stages and with or without Intermediate cooling.

In In the second stage, the chlorine contained in the exhaust gas is condensed deposited. The temperature necessary for this purpose especially after the selected pressure level or after to reach the chlorine concentration in the from the second stage leaking gas mixture. Advantageously, is the for the condensation used with a heat exchanger upstream gas-liquid contact zone, in particular below the heat exchanger is arranged, equipped, in which the resulting condensate with the entering in the second stage Gas stream is brought into contact. The contact between incoming Gas flow and the condensate takes place in countercurrent. The gas-liquid contact can optionally in the presence of internals such as mass transfer trays by ordered or disordered packing respectively. Possible suitable types of apparatus for the condensation are tube bundle heat exchangers, Plate heat exchanger, spiral heat exchanger or Block heat exchanger in horizontal or vertical arrangement.

At the the lower end of the contact zone, the condensate is in a sump collected. The composition of the condensate hangs in the essentially of the composition of the incoming gas stream, from the selected pressure and temperature level and from the Number of in the described gas-liquid contact zone in countercurrent equilibrium stages.

The typical condensation temperature is depending on the selected Pressure level in particular in the range of -20 ° C to -60 ° C.

The Chlorine concentration of the gas stream exiting at the top condenser is preferably 0 to 40 wt .-%, more preferably 0 to 5 wt .-%.

The chlorine concentration of the condensate leaving at the top condenser is preferably two 0 to 40 wt .-%, particularly preferably 0 to 5 wt .-%.

Furthermore, the new method includes optional preferred energy optimization measures such as in 2 shown.

in this connection is in a first heat exchanger behind the first stage the condensate stream from the rectification column of the third stage evaporates and thus the coming of the first stage exhaust stream cooled. Possible types of apparatus are tube bundle heat exchangers, Plate heat exchanger, spiral heat exchanger or Block heat exchanger in horizontal or vertical arrangement.

Farther the new preferred method involves the use of a recuperator, in the heat between that coming from the first stage and optional in the first above-mentioned heat exchanger already cooled exhaust stream and coming from the second stage Exhaust gas flow is exchanged. Possible suitable types of equipment for a recuperator are shell and tube heat exchangers, plate heat exchangers, Spiral heat exchanger or block heat exchanger in horizontal or vertical arrangement.

It There is also the possibility of the second stage emerging gas stream with the exiting from the second stage Mix exhaust gas flow and use the mixture in the recuperator.

In the third stage is preferred from the apparatus sump of the second Stage rectified condensate rectified. The condensate is this particular a rectification column between the reinforcing part and supplied to the driven part. In the column, the vapor stream generated in the evaporator with a portion of the condensed in the top condenser Steam, the head condensate, multi-stage and in countercurrent in contact brought. The gas-liquid contact can optionally by Mass transfer trays or by orderly or disorderly Fillings done.

Of the Top condenser can be designed in particular as a partial condenser be a discharge of inert components in the gaseous Condition to allow. The resulting condensate is then partly attributed to the column. The am Column head and present at the bottom of the column chlorine concentrations depend essentially on the evaporator supplied Energy and from the recycled to the column Condensate from. Preferably, the chlorine concentration thus set is in the withdrawn at the bottom of the column stream at 50 to 100 wt .-%, preferably 90 to 100 wt .-%.

The Invention will be closer by way of example with reference to the figures explained. Show it:

1 the flow chart of a preferred embodiment of the method according to the invention.

2 the flow chart of a preferred variant of the method according to 1 ,

3 the flow chart of another preferred variant of the method according to 1 ,

Examples

example 1

The exhaust gas flow 1 an upstream Deacon process (not shown) consisting of nitrogen, oxygen and carbon dioxide with a proportion of chlorine in the order of 10 wt .-% is brought in the first stage A with a blower k to a pressure of 35 bar (35000 hPa) ,

The condensed stream 2 is fed in the second stage B a gas-liquid contact zone b in the gas stream 2 is brought into contact with condensed chlorine. Above the gas-liquid contact zone b is a cooler a in which chlorine is condensed at a temperature of -42 ° C. In the bottom c of the gas-liquid contact zone b, the chlorine condensate is collected and as a stream 4 the third stage C supplied. The non-condensable gases are called electricity 3 discharged and, if necessary, after destruction of least amounts of residual chlorine, recycled or discarded.

The condensate 4 is fed to a rectification column d and abandoned in the central region between the reinforcement part e and the output part f. The bottom of the column d is an evaporator g and the head of a condenser h downstream.

In the column is the vapor stream generated in the evaporator g with a Part of the condensed in the top condenser h steam, the overhead condensate, in several stages and in countercurrent brought into contact. The gas-liquid contact takes place by means of mass transfer trays (not shown).

The head condenser h is designed as a partial condenser to allow the discharge of inert components in the gaseous state (current 5 ). The resulting condensate is partially recycled to the column d. The at the top of the column (Strom 5 and 6 . 1 ) and at the bottom of the column (Strom 7 ) present chlorine concentrations depend essentially on the energy supplied to the evaporator and on the amount of condensate returned to the column. The chlorine con centered in the withdrawn at the bottom of the column stream 7 is 90% by weight.

Example 2

2 is an alternative driving style again. This is in a first shell and tube heat exchanger 1 behind the fan k, the condensate stream 6 ' evaporated from the rectification column of the stage C and thus cooled from the first stage A exhaust gas stream. The pre-cooled exhaust gas flow 2 ' is passed through a recuperator (shell and tube heat exchanger i), in the heat between the exhaust stream 2 ' and the coming of the second stage B exhaust stream 3 ' is exchanged.

In addition, the gas stream leaving the second stage B becomes 5 ' with the gas flow emerging from the top condenser a 3 ' mixed and the mixture passed through recuperator i and then with the out of the tube bundle heat exchanger 1 leaking electricity 6 ' united and removed.

Example 3

3 is another alternative driving style again. Here, in a recuperator i behind the fan k heat between the stream 2 and the stream 5 exchanged. The electricity thus obtained 4 is fed directly to a rectification column d. The current 3 is discharged and reused or discarded as needed, possibly after the destruction of the smallest residual amount of residual chlorine, if any.

In the column is the vapor stream generated in the evaporator g with the in the top condenser h condensed steam, the overhead condensate, multi-stage and contacted in countercurrent. The gas-liquid contact takes place by means of mass transfer trays (not shown).

The head condenser h is designed as a partial condenser to allow the discharge of inert components in the gaseous state (current 5 ). The resulting condensate is returned to the column d. The at the top of the column (Strom 5 . 3 ) and at the bottom of the column (Strom 7 ) present chlorine concentrations depend essentially on the energy supplied to the evaporator and on the amount of condensate returned to the column. The chlorine concentration in the withdrawn at the bottom of the column stream 7 is 90% by weight.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 0406675 B1 [0005]
• US 3984523 [0005]
• - DE 2413358 [0005]

Claims (8)

A method for recovering chlorine from an exhaust gas stream, in particular the exhaust gas stream of a chemical production process, characterized in that - in a first stage A), the exhaust gas stream is brought to a pressure of at most 15 bar (15000 hPa); In a second stage B), the exhaust gas stream coming from the first stage is cooled and the chlorine contained therein is partially or completely separated by condensation together with a part of the other condensable or soluble components contained in the exhaust gas and the condensate accumulating in a zone below the condensation zone a built-up gas-liquid contact zone is brought into contact with the exhaust gas stream entering the second stage in countercurrent; - In a third stage C) coming from the second stage condensate is divided in a rectification column into a chlorine-rich bottom stream and a gaseous and a liquid, low-chlorine top stream and the chlorine-rich bottom stream is worked up to obtain chlorine. Method according to claim 1, characterized in that that the exhaust stream at least nitrogen, oxygen, carbon dioxide and chlorine. Method according to claim 1 or 2, characterized that in the first stage the exhaust gas flow to a pressure of 20 to 60 bar, preferably 30 to 40 bar, is set. Method according to at least one of the claims 1 to 3, characterized in that the condensation temperature in the second and the third stage -20 ° C to -80 ° C is. Method according to at least one of the claims 1 to 5, characterized in that between the first Stage coming gas stream and coming from the third stage Condensate exchanged heat and the condensate from the third stage is evaporated. Method according to at least one of the claims 1 to 6, characterized in that between the second Stage leaking gas stream and the entering in the second stage Gas stream heat is exchanged. Method according to at least one of the claims 1 to 6, characterized in that first of the the second and third stage mixed gas streams mixed will be followed by the one entering the second stage Gas stream heat exchange Method according to at least one of the claims 1 to 7, characterized in that the chlorine-containing exhaust gas stream from a production process for the production of chlorine from hydrogen chloride and oxygen is derived, especially a catalyzed gas phase oxidation of hydrogen chloride or a non-thermal reaction of Hydrogen chloride and oxygen.